It depends on what you're wanting to do. The core BASIC dialects were only subtly different however the hardware wasn't and it was the interfacing with the hardware where BASIC used to vary the most. This might take up a large chunk of your code (since back in those days you wrote the game engines etc as part of the game) but it's still only a relatively small subset of the BASIC language once you factor in syntax, operators, keywords, etc. To that end you could in fact write a text adventure game in BASIC that would run on multiple different platforms without modification (and I done just that in the past). But it would be the BASIC equivalent of a Bourne Shell (.sh) script.
https://en.wikipedia.org/wiki/Input_(magazine)
They did not do things subtly differently, rather completely different, depending on the model.